Heroin addiction can have devastating social, medical and economic consequences. Methadone maintenance is an effective treatment for heroin addiction, but only about 20 percent of opiate dependent individuals receive it. Naltrexone is an opiate antagonist that could provide an extraordinarily effective alternative for many individuals. However, its utility has been limited because most individuals refuse it. A randomized study is planned over 5 years to evaluate the effectiveness of the Therapeutic Workplace in promoting naltrexone ingestion and abstinence in unemployed opiate-dependent injection drug users. The Therapeutic Workplace is a novel employment-based intervention that uses salary for work to reinforce clinically important behavior change. Drug abuse patients are hired and paid in this model workplace. To promote clinically important behaviors, salary is arranged contingent both on work and on the emission of those behaviors. Participants will be offered an opioid detoxification and naltrexone induction. Participants who complete the naltrexone induction will be randomly assigned to one of three groups. All groups will be invited to work in the Therapeutic Workplace and prescribed naltrexone for 26 weeks. The groups will differ in the contingencies imposed to work and earn salary. "Work Plus Naltrexone Contingency" participants will be required to ingest naltrexone to work, and will receive a brief pay decrease for missing a dose. "Work Plus Naltrexone and Abstinence Contingency" participants will be required to ingest naltrexone to work, and will receive a brief pay decrease for missing a dose of naltrexone or for providing an opiate or cocaine positive urine sample. "Work Plus Naltrexone Prescription" participants will be prescribed naltrexone, but will not be required to ingest it to work. Critical measures of opiate and cocaine use and HIV risk behaviors will be assessed. This study will provide a rigorous evaluation of a novel employment based intervention, the Therapeutic Workplace, to promote naltrexone ingestion and drug abstinence in a population of injection drug users who are at considerable risk of spreading or contracting HIV infection.